The present invention relates to a rolling mill equipped with an on-line roll grinding system, and more particularly to an on-line roll grinding system for effectively grinding mill rolls on-line without undergoing influences of vibration of work rolls.
Generally, when slabs are rolled by work rolls of a strip rolling mill, there occurs a periphery difference between the rolling zone and the unrolling zone because only the former is abraded or worn away. This imposes such restrictions upon the rolling operation as necessity of rolling slabs in order of wide ones to narrow ones. To solve that problem, there have been proposed various techniques and control methods in relation to on-line roll grinders.
For example, xe2x80x9cDevelopment of On-Line Roll Grindersxe2x80x9d, Mitsubishi Giho, Vol. 25, No. 4, 1988, discloses a technique that a plurality of cup grinding stones are arranged along one work roll and mounted to a one-piece frame, the frame being always moved in its entirety over a certain range, and the cup grinding stones are not positively driven to rotate but passively driven with the aid of torque of the work roll, thereby grinding the entire surface of the work roll (hereinafter referred to as first prior art).
Also, JP, U, 58-28705 discloses a technique that one roll grinding unit is disposed for one work roll, contact rolls serving as position sensors are held in contact with neck portions at both ends of the work roll on the side thereof opposite to the roll grinding unit, the position sensors detecting an offset of the work roll, and a shifting device is controlled to move a grinding wheel following the detected offset (hereinafter referred to as second prior art).
Further, xe2x80x9cOn-Line Constant Pressure Grinding for Work Rollsxe2x80x9d, Proceedings of 1992 Spring Lecture Meeting of Precision Engineering Society of Japan, reports an experimental result of forming an abrasive layer of a cup grinding stone using abrasives of cubic boron nitride (CBN), arranging a spindle of the grinding stone perpendicularly to the axis of a work roll, and grinding the work roll (hereinafter referred to as third prior art).
In addition, JP, U, 58-28706 and JP, U, 62-95867 disclose a technique that a cup grinding stone arranged substantially perpendicular to a work roll is mounted to a spindle slidably in its axial direction, and the grinding stone is axially supported at its backside by an elastic body directly or via a boss, thereby absorbing vibration of the work roll (hereinafter referred to as fourth prior art).
Meanwhile, in strip rolling machines, it has been conventionally proposed to measure the profile of a work roll and control the crown and shape of a strip by utilizing the measured profile. As a technique for measuring the profile of the work roll, an on-line roll profile meter has been developed which employs a ultrasonic profile meter. The system configuration of this profile meter is described in xe2x80x9cDevelopment of On-Line Roll Grinding System with Profile Meterxe2x80x9d, Mitsubishi Giho, Vol. 29, No. 1, 1992. In this system, a column of water is produced between a probe with a ultrasonic profile meter built therein and a work roll, and the spacing from the probe to the work roll is determined based on the time required for pulsatory ultrasonic waves emitted from the probe to reciprocate between the probe and the surface of the work roll (hereinafter referred to as fifth prior art).
Work rolls of a rolling mill are each held by bearings assembled in metal chocks and rotated at a high speed. The metal chocks each have gaps in its inner and outer circumferences for facilitating replacement of the work roll and the bearing. During rotation, therefore, the work roll is rotated while moving back and forth in the gaps. In addition, since a cylindrical portion of the work roll undergoes an offset with respect to the bearings, the work roll is vertically moved by a screwdown device during strip rolling. As a result of those movements combined with each other, the work roll is rotated while vibrating at all times.
Generally, when grinding cylindrical works, the work to be ground is supported by a tail stock rotating with high precision to carry out the grinding under a condition that vibration of the work is suppressed to be as small as practicable. In an attempt to grind the work roll while rolling a strip in the rolling mill, however, it is impossible to carry out the grinding under a condition of very small vibration like works in the above ordinary case. During the rolling, the work roll is rotated while vibrating usually with an amplitude of 20 xcexcm to 60 xcexcm and an acceleration of 1G to 2G. An on-line roll grinding system must precisely grind the work roll under such a condition.
With the above first to third prior arts, when they are applied to the grinding of such a vibrating work roll, there produce irregularities on the surface of the work roll due to chattering marks. Also, the grinding stone or wheel is remarkably worn away with the impact force caused by chattering, and its service life is so shortened as to require more frequent replacement. Further, it is difficult to control the contact force in the case of grinding the work roll into a predetermined profile.
The above fourth prior art is designed to absorb the vibration of the work roll by the elastic body. With this prior art, however, since the entire grinding stone including a stone base is supported by the elastic body and moved back and forth, there accompanies a problem that the movable mass of the grinding stone, i.e., the weight of a portion which is forced to move following the vibration, is great. Even in the case of using, as the abrasive layer of the grinding stone, abrasives of cubic boron nitride (CBN) which has a high Grinding ratio, the movable mass of the grinding stone supported by the elastic body and moving back and forth is at least more than 5 Kg, including the stone itself of which diameter is assumed to be 250 mm, slide bearings and sealing parts. Supposing that an allowable value of change in the contact force between the work roll and the grinding stone is 4 Kgf and the amplitude of vibration of the work roll is 30 xcexcm, the spring constant of the elastic body must be set to 130 Kgf/mm. Under the above conditions, the natural frequency of the movable portion including the elastic body is calculated to be 80 c/s. The movable portion including the elastic body, which has such a low natural frequency, is caused to resonate with the vibration of the work roll, thereby producing chattering marks on the roll surface and accelerating abrasion of the grinding stone. If the stone size is reduced to make the movable mass smaller, the grinding ability would be lowered to a large extent.
The cup grinding stone is slidable in the axial direction of the spindle and supported at its backside by the elastic body. During the roll grinding, however, a coolant, grinding dust and the like are scattered around the grinding stone, and these foreign matters may enter clearances between the grinding stone and the spindle to impede smooth movement of the grinding stone. It is therefore difficult for the elastic body to stably develop its function for a long period of time.
The above first and second prior arts also have the following problem. The unrolling zone of the work roll is not subjected to abrasion by the strip and hence should be ground to a larger extent than the rolling zone. With the above first embodiment, however, because the circumferential speed of the cup grinding stone is limited by the rotational speed of the work roll, the grinding rate can be controlled only by changing the contact force in the case of grinding the unrolling zone to a larger extent. This imposes a limitation upon the grinding rate, making it difficult to keep a constant roll profile for a long period of time.
With the above second embodiment, since the spindle is arranged perpendicularly to the work roll, the abrasive layer of the grinding wheel contacts the work roll at two right and left points of its annular abrasives surface and the work roll is simultaneously ground at those two points. Therefore, if the work roll has a periphery difference, the two grinding surfaces interfere with each other to cause chattering marks. Also, the contact at two points between the grinding wheel and the work roll leads to a difficulty in controlling the contact force therebetween. Additionally, the position sensors have a problem of reliability under severe environment of rolling machines. From these reasons, the above second embodiment has not yet been put into practice.
Measurement of a roll profile will now be considered. After a strip is rolled by work rolls, the work rolls are each worn away about 2 xcexcm/radius per coil of a hot rolling steel strip, for example, in the zone where the strip is rolled. Due to this wear and the thermal crown resulted from an increase in the roll diameter caused by the heat of the strip, the profile of the roll surface is changed over the entire length of a roll barrel. If the roll profile can be correctly measured, the on-line roll grinder provided in the rolling mill can grind the work roll into the roll profile optimum for the rolling. Heretofore, it has been regarded to be difficult to correctly measure the roll profile of the work roll, which is vibrating and sprayed with a large amount of roll coolant at all times, in the rolling mill, i.e., on-line.
As known from the above fifth prior art, there has been developed an on-line profile meter of the type that a column of water is produced between a probe and a work roll for determining the spacing from the probe to the work roll based on the time required for ultrasonic waves to reciprocate between the probe and the surface of the work roll. However, because of measuring the time during which ultrasonic waves reciprocate through the very short distance, the measure time is also very short and the profile distance is on the order of microns. There is hence a fear that even a small error of the measured time may result in a large profile error. Particularly, in the case of using the ultrsonic profile meter for a long period of time, even if the state of the column of water between the probe and the roll is so changed as to cause an error in the measurement, it is difficult to find such an error. Although the ultrasonic profile meter can always correctly measure the roll profile in principles, there is a difficulty in maintaining high precision at all times in practice when the ultrasonic profile meter is used for a long period of time under the severe environment as mentioned above. The presence of plural measuring probes also makes it difficult to perform compensation.
A first object of the present invention is to provide a rolling mill equipped with an on-line roll grinding system and a grinding wheel for the on-line roll grinding system in which vibration from a work roll is absorbed to enable precise grinding with good roughness of the roll surface without giving rise to any chattering marks.
A second object of the present invention is to provide a rolling mill equipped with an on-line roll grinding system and a grinding wheel for the on-line roll grinding system in which the profile of a work roll can be correctly measured by a roll profile meter provided integrally with the on-line roll grinding system.
To achieve the above first object, in accordance with the present invention, there is provided a rolling mill equipped with an on-line roll grinding system comprising a plain type grinding wheel positioned to face one of a pair of mill rolls for grinding one said mill roll, grinding wheel drive means for rotating said grinding wheel through a spindle, grinding wheel movement means for pressing said grinding wheel against said mill roll, and grinding wheel traverse means for moving said grinding wheel in the axial direction of said mill roll, wherein said grinding wheel comprises a plain wheel attached to said spindle and an abrasive layer fixed to one side of said plain wheel, said plain wheel having an elastically deforming function to absorb vibration transmitted from said mill roll.
In the above on-line roll grinding system, preferably, said grinding wheel is arranged such that a contact line between said abrasive layer and said mill roll is defined only in one side as viewed from the center of said grinding wheel, and more preferably, said grinding wheel is arranged with said spindle inclined by a small angle relative to the direction perpendicular to an axis of said mill roll, so that a contact line between said abrasive layer and said mill roll is defined only in one side in the roll axial direction as viewed from the center of said grinding wheel.
Preferably, said abrasive layer is annular in shape, and said abrasive layer contains super abrasives, i.e., cubic boron nitride abrasives and/or diamond abrasives.
Also, said plain wheel preferably has a spring constant of 1000 Kgf/mm to 30 Kgf/mm, and more preferably a spring constant of 500 Kgf/mm to 50 Kgf/mm.
Preferably, said abrasive layer contains cubic boron nitride abrasives, said abrasives having a concentration of 50 to 100 and a grain size of 80 to 180, and a resin bond is used as a binder for said abrasives.
Preferably, said on-line roll grinding system further comprises load detecting means for measuring the contact force between said grinding wheel and said mill roll, and control means for controlling said grinding wheel movement means to optionally change the contact force measured by said load detecting means so that a grinding rate of said grinding wheel on said mill roll is changed, for thereby grinding said mill roll into a predetermined roll profile.
Said on-line roll grinding system may further comprise load detecting means for measuring the contact force between said grinding wheel and said mill roll, and control means for controlling said grinding wheel movement means so that the contact force measured by said load detecting means is held constant, and for simultaneously controlling said grinding wheel traverse means to optionally change a traverse speed of said grinding wheel in the roll axial direction so that a grinding rate of said grinding wheel on said mill roll is changed, for thereby grinding said mill roll into a predetermined roll profile.
Preferably, said grinding wheel movement means comprises a rotation drive source, and a ball screw mechanism or a gear mechanism having a small backlash and converting rotation of said rotation drive source into axial movement of said grinding wheel movement means for moving said grinding wheel back and forth relative to said mill roll.
Preferably, said on-line roll grinding system comprises at least two grinding head units for each of said mill rolls, each of said two grinding head units including said grinding wheel, said grinding wheel drive means, said grinding wheel movement means and said grinding wheel traverse means, whereby said two grinding head units can grind said mill roll independently of each other.
In this case, said on-line roll grinding system preferably further comprises control means for stopping said grinding wheel traverse means of two said grinding head units at different positions so that a grinding overlap zone produced when grinding said mill roll by said two grinding head units is distributed in the roll axial direction.
Preferably, said grinding wheels of two said grinding head units are arranged with respective spindles inclined by a small angle in opposite directions relative to the direction perpendicular to an axis of said mill roll, so that respective contact lines between said abrasive layers and said mill roll are each defined only in one corresponding roll end side in the roll axial direction as viewed from the center of said grinding wheel.
To achieve the above second object, in accordance with the present invention, there is provided a rolling mill equipped with an on-line roll grinding system, wherein said on-line roll grinding system further comprises displacement detector means for measuring a stroke of said grinding wheel in the roll axial direction given by said grinding wheel traverse means, load detecting means for measuring the contact force between said grinding wheel and said mill roll, and an on-line profile meter including first profile calculating means for calculating a profile of said mill roll from both the contact force measured by said load detecting means and the stroke measured by said displacement detector means under a condion of keeping a stroke of said grinding wheel movement means constant.
Also, to achieve the above second object, in accordance with the present invention, there is provided a rolling mill equipped with an on-line roll grinding system, wherein said on-line roll grinding system further comprises first displacement detector means for measuring a stroke of said grinding wheel movement means, second displacement detector means for measuring a stroke of said grinding wheel in the roll axial direction given by said grinding wheel traverse means, load detecting means for measuring the contact force between said grinding wheel and said mill roll, and an on-line profile meter including second profile calculating means for calculating a profile of said mill roll from both the stroke measured by said first displacement detector means and the stroke measured by said second displasemsent detector means under a condition of keeping the contact force measured by said load detecting means constant.
In the above on-line roll grinding system, said on-line profile meter preferably further includes means for calculating a deviation of a profile of said mill roll measured by an off-line profile meter from the profile of said mill roll determined by said first or second profile calculating means, determining from said deviation an error in parallelism of the direction of movement of said grinding wheel by said grinding wheel traverse means with respect to said mill roll, and compensating the roll profile determined by said first or second profile calculating means based on the determined error in parallelism.
Preferably, said on-line profile meter further includes means for calculating a deviation of the profile of said mill roll determined by said first or second profile calculating means from a preset target roll profile, and controlling at least one of said grinding wheel movement means and said grinding wheel traverse means based on the calculated deviation so that a grinding rate of said grinding wheel on said mill roll is changed, for thereby grinding said mill roll to be identical with said target roll profile.
In this case, said control means preferably controls said grinding wheel movement means to optionally change the contact force measured by said load detecting means for thereby changing said grinding rate.
Alternatively, said control means may control said grinding wheel movement means so that the contact force measured by said load detecting means is held constant and, simultaneously, controls said grinding wheel traverse means to optionally change a traverse speed of said grinding wheel in the roll axial direction for thereby changing said grinding rate.
Also, said rolling mill preferably further comprises at least one of roll bender means for applying bender forces to said mill roll, roll shifting means for shifting said mill roll in the axial direction and roll crossing means for making said pair of mill rolls crossed each other, and control means for controlling at least one of the bender forces of said roll bender means, a shift position set by said roll shifting means and a cross angle set by said roll crossing means based on the profile of said mill roll measured by said first or second profile calculating means so that the strip crown approaches a target strip crown.
Further, in said rolling mill, said on-line roll grinding system preferably further comprises control means for measuring an inclination of the axis of said mill roll and controlling said grinding wheel movement means and said grinding wheel traverse means so that said grinding wheel moves following a target roll profile in consideration of the inclination of the axis of said mill roll. In this case, preferably, said on-line roll grinding system further comprises presser means for fixing metal chocks supporting both ends of said mill roll, and holding the inclination of the axis of said mill roll constant during the grinding.
In the above on-line roll grinding system, preferably, said grinding wheel, said grinding wheel drive means, said grinding wheel movement means and said grinding wheel traverse means constitute one grinding head unit, and said on-line roll grinding system further comprises a reference small-diameter zone formed on at least one end of said mill roll and having a known diameter smaller than the diameter of a roll barrel, and a displacement meter provided on said grinding head unit for measuring a distance from said grinding head unit to said mill roll.
In the above rolling mill, preferably, said mill roll is a work roll, and said grinding wheel, said grinding wheel drive means, said grinding wheel movement means and said grinding wheel traverse means constitute a grinding head unit for grinding said work roll. Alternatively, said mill roll is a backup roll, and said grinding wheel, said grinding wheel drive means, said grinding wheel movement means and said grinding wheel traverse means constitute a grinding head unit for grinding said backup roll.
Preferably, said on-line roll grinding system further comprises a reference small-diameter zone formed on at least one end of said mill roll and having a known diameter smaller than the diameter of a roll barrel, and roll diameter calculating means for pressing said grinding wheel against said mill roll at respective positions in said reference small-diameter zone and said roll barrel such that the contact force between said grinding wheel and said mill roll has the same value, determining a periphery difference between said reference small-diameter zone and said roll barrel from a difference in displacement of said grinding wheel at that time, and determining a roll diameter in said roll barrel from the determined periphery difference and the known roll diameter in said reference small-diameter zone.
Furthermore, to achieve the above first and second objects, in accordance with the present invention, there is provided a grinding wheel for an on-line roll grinding system comprising a plain wheel and an abrasive layer fixed to one side of said plain wheel and formed of super abrasives, said plain wheel having an elastically deforming function to absorb vibration transmitted from a mill roll.
Operation of the present invention thus constructed is as follows.
First, in the present invention, with an elastically deforming function imparted to the plain wheel as a part of the plain type grinding wheel, when the grinding wheel is pushed upon vibration of the mill roll, the plain wheel is deflected to momentarily absorb the vibration transmitted from the mill roll. Accordingly, fluctuations in the contact force between the abrasive layer and the mill roll are held down within a small range of the elastic force fluctuating upon the deflection of the plain wheel, thereby eliminating the occurrence of chattering marks. Further, an elastically deforming function is imparted to the plain wheel serving as a base for supporting the abrasive layer so that the abrasive layer is integral with a member having the elastically deforming function. Therefore, only both the abrasive layer and the plain wheel provide the mass forced to move upon the vibration from the mill roll, whereby the movable mass can be very small and the natural frequency of the grinding wheel can be raised. Consequently, the vibrating mill roll can be correctly ground for a long period of time without causing any chattering marks due to resonance.
With the grinding wheel arranged such that the contact line between the abrasive layer and the mill roll is defined only in one side as viewed from the center of the grinding wheel, the plain wheel is allowed to deflect in cantilever fashion when pressed against the mill roll, whereby the elastically deforming function of the plain wheel is effectively developed to easily absorb the vibration transmitted from the mill roll. Further, since the contact line is defined in only one side of the wheel center, the occurrence of chattering marks is prevented and contact force control (described later) can be performed properly.
With the abrasive layers formed of super abrasive grains, particularly, cubic boron nitride abrasives or diamond abrasives, the grinding wheel has a grinding ratio more than 100 times that of the grinding wheel made of aluminum oxide (Al2O2) abrasives or silicon carbide (SiC) abrasives, resulting in that the grinding can be continued for a long period of time with a small weight of the grinding wheel. Consequently, the movable mass of the grinding wheel is further reduced, which is effective in preventing resonance during the grinding, reducing the exchange pitch of the grinding wheel, and improving productivity of the rolling mill.
As to the spring constant of the plain wheel, if the spring constant is too large, the chattering marks are caused, the grinding ratio is lowered, and further the abrasive layer is soon worn away thoroughly. Also, if the spring constant of the plain wheel is too large, the contact force between the abrasive layer and the mill roll is so largely fluctuated as to impose a difficulty in controlling the grinding rate due to the contact force. Through the studies conducted by the inventors, it has been found that by setting the spring constant of the plain wheel to be not larger than 1000 Kgf/mm, preferably 500 Kgf/mm, it is possible to prevent the abrasive layer from being soon worn away thoroughly, and use the grinding wheel continuously for not less than 5 days once exchanged.
On the contrary, if the spring constant is small, the contact force imposed on the grinding wheel due to the vibration of the mill roll is less fluctuated. The grinding ratio is therefore raised, but sensitivity of detecting the contact force is lowered and accuracy of grinding control and roll profile measurement both based on the contact force is degraded. Also, the smaller spring constant of the plain wheel means that the plain wheel is thinner and the grinding wheel is deflected to a larger extent with the same contact force, causing cracks in the plain wheel even with the contact force necessary for the grinding. Through the studies conducted by the inventors, it has been found that by setting the spring constant of the plain wheel to be not less than 30 Kgf/mm, the plain wheel can be prevented from cracking, and by setting the spring constant to be not less than 50 Kgf/mm, even load fluctuations generated with a periphery difference of 10 xcexcm can be detected.
As to compositions of the abrasive layer, in order to keep the grinding ability constant and stabilize the grinding roughness without dressing in on-line roll grinding, it is required for the super abrasive grains of the abrasive layer to be spontaneously edged at a constant rate. Proper spontaneous edging of the super abrasive grains needs adjustment of the load imposed on one super abrasive grain. Through the studies conducted by the inventors, it has been found that by setting density, i.e., concentration, of the super abrasive grains contained in the abrasive layer within the range of 50 to 100 and using a resin bond as a binder, the super abrasive grains are easily spontaneously edged, the service life of the abrasive layer is not shortened, and hence continuous grinding is enabled without dressing. It has been also found that the size of the super abrasive grains, i.e., the grain size, is required to be in the range of 80 to 180 for obtaining the surface roughness of the mill roll in the range of 0.3 to 1.5 xcexcm in average.
By continuously measuring the contact force between the mill roll and the grinding wheel and then changing the contact force, the grinding rate of the grinding wheel on the mill roll per unit time is changed. Thus, by measuring the contact force at all times and controlling the position of the grinding wheel by the grinding wheel movement means so that the contact force is held constant, the mill roll can be ground by the same dimension all over its cylindrical barrel. In other words, it is possible to grind the enter length of the mill roll while maintaining its original profile.
Also, by controlling the contact force in such a manner as to increased and decrease, the mill roll can be ground into an arbitrary roll profile. Further, by optionally controlling the traverse speed of the grinding wheel in the roll axial direction while controlling the contact force to be kept constant, the mill roll can also be ground into an arbitrary roll profile.
Unless the grinding wheel movement means for pressing the grinding wheel against the mill roll is constituted by using a mechanism having a high spring constant, there may cause chattering marks. As grinding wheel movement means which is compact and has a high spring constant, optimum one is a mechanism in which a baklashless pre-loaded ball screw is driven by an electric motor. This mechanism is also able to hold the position of the grinding wheel constant during the grinding and to finely move the grinding wheel back and forth.
When the grinding wheel is moved in the roll axial direction for grinding the mill roll, it is required to grind the unrolling zone to a larger extent than the rolling zone for eliminating a periphery difference between the unrolling zone and the rolling zone. The unrolling zone exists at each of both ends of the mill roll. In view of that, a plurality of grinding head units each including the grinding wheel, the grinding wheel drive means, the grinding wheel movement means and the grinding wheel traverse means are disposed to be movable independently of each other. Normally, two units are moved to remain in the respective unrolling zones at both roll ends for grinding them. Once per several times, the grinding head units are moved to the rolling zone of the mill roll for grinding a fatigue layer on the surface therein. Thus, corresponding to wear of the rolling zone caused by rolling a strip, the unrolling zones are ground by the grinding wheel so that the roll profile free from a periphery difference can be maintained.
When a plurality of grinding head units are arranged to be movable independently of each oter for grinding a mill roll, there occurs an overlap zone on the mill roll where the roll surfaces ground by adjacent grinding wheels overlap with each over. The grinding wheel traverse means are stopped at different positions so that the overlap zone will not always produce at the same posision, thereby distributing the overlap position.
As mentioned above, by making the contact line between the grinding wheel and the mill roll defined at one point, it is possible to carry out satisfactory grinding under constant conditions. In the present invention, therefore, the spindle of the grinding wheel is inclined by a small angle relative to a line perpendicular to the axis of the mill roll. By so arranging, in the on-line roll grinding system having a plurality of grinding wheels, there may occur an interference between the end of the grinding wheel and a housing if the spindles are inclined in the same direction at both ends of the mill roll. Such an interference in the grinding can be avoided by arranging the spindles of the grinding head units positioned at both ends of the mill roll to be inclined in opposite directions. Accordingly, the grinding wheels can be freely moved to the respective ends of the mill roll, and there is no need of particularly considering the dimension between the roll end and the housing.
Further, in the on-line profile meter having the first profile calculating means of the present invention, the grinding wheel is pressed by the grinding wheel movement means against the rotating mill roll to deflect the plain wheel in a certain amount, following which the grinding wheel movement means is stopped and the contact force between the mill roll and the grinding wheel at that time is measured by the load detecting means. Then, while moving the grinding wheel by the grinding wheel traverse means in the axial direction of the mill roll, the stroke (axial position) of the grinding wheel is measured by the displacement detector means and the contact force is measured by the load detecting means.
Since the abrasive layer of the grinding wheel is supported by the plain wheel having an elastically deforming function and the plain wheel has a fixed spring constant, the larger contact force increases a deflection of the plain wheel. Conversely, the smaller contact force reduces a deflection of the plain wheel. On the other hand, if the axis of the mill roll and the on-line roll grinding system or the grinding head units are parallel to each other, the plain wheel of the grinding wheel is deflected to a larger extent with a larger diameter of the mill roll and to a smaller extent with a smaller diameter of the mill roll on condition that the grinding wheel movement means is kept fixed.
In the first profile calculating means, therefore, the deflection of the plain wheel is determined from the value (contact force) measured by the load detecting means and processed to be correspondent to respective positions in the roll axial direction, thereby obtaining a profile of the mill roll.
Moreover, in the on-line profile meter having the second profile calculating means of the present invention, the grinding wheel is pressed by the grinding wheel movement means against the rotating mill roll to deflect the plain wheel in a certain amount, and then the grinding wheel movement means is controlled so that the deflection of the plain wheel (i.e., the contact force) is always held constant. While measuring the stroke of the grinding wheel in the axial direction of its spindle by the first displacement detector means, the grinding wheel is moved in the roll axial direction by the grinding wheel traverse means and the stroke (axial position) of the grinding wheel is measured by the second displacement detector means. Thus, in the second profile calculating means, the stroke of the grinding wheel in the axial direction of its spindle is determined from the measured value of the first displacement detector means and processed to be correspondent to respective positions in the roll axial direction, thereby obtaining a profile of the mill roll.
The on-line roll grinding system is initially installed such that the direction of traverse movement along the roll axial direction is in parallel to the axis of the mill roll. But, there is a fear in hot rolling mills that parallelism between them may change for a long period of time due to the heat of strips. Unless such a change in parallelism is compensated, the roll profile measured as mentioned above cannot be said as a true profile. The compensation means provided in the on-line profile meter compensates the error in parallelism and enables the more precise profile measurement.
More specifically, a mill roll is ground by an off-line roll grinder installed in a roll shop, and its roll profile after the grinding is measured by an off-line roll profile meter. After assembling the mill roll into the rolling mill, a profile of the mill roll is measured by using the first or second profile calculating means of the on-line roll profile meter. Then, a deviation (difference) between both the profile values measured by the off-line and on-line roll profile meters is determined and, from this determined deviation, an error in parallelism of the on-line roll grinding system or the grinding head units with respect to the roll axial direction is determined. Since then, at the time of measuring a profile of the mill roll by using the first or second profile calculating means, the above error in parallelism is subtracted from the measured values obtained as mentioned above, thereby compensating the measured values to determine the correct measured values.
In the control means for grinding the mill roll to be identical with a target roll profile, after determining a profile of the mill roll by the first or second profile calculating means, a deviation of the determined profile of the mill roll from a preset target roll profile is calculated. The grinding wheel movement means is controlled such that the grinding wheel is pressed against the mill roll by a stronger force in the roll radial direction (at the roll axial position) in which the above deviation is large, thereby controlling the grinding rate on the mill roll so that the mill roll is ground into the target roll profile. Alternatively, while controlling the contact force between the mill roll and the grinding wheel to be held constant, the traverse speed of the grinding wheel in the roll axial direction may be changed to vary the grinding rate on the mill roll. In this case, too, the mill roll is ground into the target roll profile.
After determining a profile of the mill roll by the first or second profile calculating means, the determined data is input to a system computer for controlling the entire rolling mill and, based on the input data, roll benders provided in the rolling mill is operated to apply bending forces to the mill rolls, thereby improving the profile of a hot strip. When the rolling mill has roll shifting means for shifting the mill roll in the axial direction or roll crossing means for making the mill rolls crossed each other, the profile of a hot strip may be improved by controlling such means. By so using the measured roll profile as control data for the roll benders, the roll shifting means or the roll crossing means, high-accurate strip crown control is enabled.
By moving the grinding head unit in the roll axial direction while keeping the distance between the axis of the mill roll and the distal end surface of the abrasive layer constant, the mill roll is ground to have the same diameter over its entire length. By moving the grinding head unit in such a manner as to optionally change the distance between the axis of the mill roll and the distal end surface of the abrasive layer, the contact force between the mill roll and the grinding wheel is increased at the position providing the shorter distance where the mill roll is ground to a larger extent. On the contrary, the contact force between the mill roll and the grinding wheel is decreased at the position providing the longer distance where the mill roll is ground to a smaller extent. Thus, for optionally creating and maintaining a profile of the mill roll, the grinding wheel movement means is moved to control the distance between the axis of the mill roll and the distal end surface of the abrasive layer such that the distal end surface of the abrasive layer draws the same path as the target roll profile of the mill roll.
By measuring an inclination of the axis of the mill roll and grinding the mill roll while controlling the grinding wheel movement means and the grinding wheel traverse means such that the distal end surface of the abrasive layer moves along the target roll profile of the mill roll in consideration of the inclination, even if the axis of the mill roll is inclined, the correct roll profile compensated for the inclination can be always maintained.
When the work rolls is continuously ground for a long period of time, there may occur a difference in diameter between the upper and lower rolls, i.e., a diameter difference. If such a diameter difference is increased, values of rolling torque necessary for the upper and lower rolls become so different as to impose undue forces on the spindles and so forth, which may result in a trouble. To prevent such a trouble, the system is usually controlled so that the diameter difference is kept within 0.2 mm/diameter.
By forming a reference small-diameter zone having a known roll diameter in at least one end of the mill roll, and measuring a periphery difference between the reference small-diameter zone and the roll barrel by a displacement meter, the correct roll diameter can be always determined. By making such measurement on the upper and lower rolls, the diameter reference can be monitored on-line.
Also, by measuring the roll diameter at both ends of the mill roll, whether the mill roll is tapered or not in the roll axial direction after the grinding (i.e., cylindricity) can be confirmed.
Further, by pressing the grinding wheel against the mill roll at respective positions in the reference small-diameter zone and the roll barrel zone so that the contact force between the grinding wheel and the mill roll has the same value, and determining a periphery difference between the reference small-diameter zone and the roll barrel from the difference between two strokes of the grinding wheel measured at the respective positions at that time, the roll diameter can be measured without using any displacement meter.
In hot rolling mills, while work rolls are worn away due to contact with hot strips, backup rolls supporting the work rolls also develop a fatigue layer on their roll surfaces because the backup rolls are contacted with the work rolls under high contact forces. By providing the on-line roll grinding system on each of the backup rolls as well, the fatigue layer on the backup roll surfaces can be easily removed.